This application claims the priority of German application 198 36 135.1, filed in Germany on Aug. 10, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an arrangement for a ring spinning machine for condensing a drafted but untwisted fiber strand, comprising a drum, having a perforated outer sleeve, for transporting the fiber strand through a condensing zone, which is limited at its exit side by a nipping point which nips the fiber strand, also comprising a suction device arranged in the inside of the drum, which suction device comprises a suction slit extending essentially in transport direction of the fiber strand.
In an arrangement of this type (German published patent application 197 11 466), the perforated drum is at the same time the front roller of a drafting assembly. The condensing zone is located thus on the periphery of the drum and is defined by two nipping points formed together with the drum. The first nipping point is located on the front top roller of the drafting assembly, the second nipping point at an extra nipping roller, which functions at the same time as a twist block against the spinning twist imparted by a ring spindle, so that the condensing zone is free of spinning twist. The outer sleeve of the drum must permit the draft at the front roller pair of the drafting assembly. The outer sleeve is therefore quite thick-walled, which inevitably means that the holes of the perforation cannot exceed a minimum diameter. This results in the condensing zone being subjected to a relatively inhomogenous suction air stream, which is disadvantageous for the condensing effect.
The condensing of the drafted, but still spinning twist-free fiber strand serves the purpose of bundling the fiber strand before it is imparted a spinning twist, in that outwardly projecting edge fibers are rolled in around the core strand. The fiber strand becomes less hairy, the usual spinning triangle is reduced to a great extent and the spun yarn becomes with better substance utilization more homogenous, smoother and tear resistant overall.
It is an object of the present invention to make the suction air stream, effective in the condensing zone, more homogenous and thus to increase the condensing effect.
This object has been achieved in accordance with the present invention in that the outer sleeve forms a supporting skeleton for a thin sieve belt, which covers openings present in the outer sleeve in the area of the suction slit.
Deviating from prior art, the outer sleeve is no longer provided with a plurality of bore holes having a relatively large diameter, but is rather in the form of a skeleton, which comprises large, ladder-like openings over the suction slit. These openings are covered by a thin, close-meshed sieve belt, which is applied to the outer sleeve, so that a very fine and close-meshed perforation for the suction air stream arises, which makes the suction air stream very homogenous. It has been shown, namely, that the more close-meshed the perforation, the better the quality of the spun yarn. As the thin sieve belt is not capable of taking up the necessary nipping pressure at the nipping points itself, the openings of the skeleton must be sufficiently narrow. The openings are therefore advantageously narrow cross slits which are covered by the close-meshed sieve belt. The sieve belt thus cannot yield to the nipping pressures in the area of the openings.
If desired the sieve belt can also be drawn onto a ladder-like skeleton belt, which in turn is adhered or welded to the outer sleeve of the drum. This is then in particular possible when a suitable synthetic fiber is chosen.
The sieve belt is preferably in the form of a woven fabric made of polyamide filaments, so that the sieve belt can also be stiffened at its edges by means of heating. In this embodiment of the present invention, the sieve belt is sufficiently wear resistant.
When the woven belt is provided with a suitable sealable coating on its longitudinal edges, the sieve belt can be applied to the outer sleeve of the drum in an exchangeable way. The adhering effect by means of sealing should only be so strong as to permit the sieve belt to be easily removed without great use of force.